1. Field of the Invention
The present general inventive concept relates to an inkjet print head and a method of manufacturing the same, and more particularly, to an inkjet printhead and a method of manufacturing the same that can improve reliability and print quality of an image.
2. Description of the Related Art
Generally, inkjet printers print an image of a predetermined color by discharging ink from a printhead at a desired location on a print medium. The inkjet printers are classified into shuttle-type inkjet printers and line printing type inkjet printers. In the shuttle-type inkjet printers, a printhead performs printing operations by moving up and down perpendicular to a transport direction of a print medium. The line printing type inkjet printers, which are currently being developed to perform high speed printing, include one or plural printheads having a width corresponding to a width of the print medium. The printhead, which is fixed, performs printing as the print medium moves. An array printhead, in which a plurality of printheads are arranged in a predetermined pattern, is commonly-used in the line printing type inkjet printers.
Inkjet printheads are largely categorized into two types depending on an ink droplet ejection mechanism used by the printheads: a thermally-driven inkjet printhead, in which a heat source is employed to form and expand bubbles in ink causing ink droplets to be ejected, and a piezoelectrically driven inkjet printhead, in which a piezoelectric material deforms to exert pressure on ink causing ink droplets to be ejected.
The ink ejection mechanism in the thermally driven inkjet printhead is as follows. When a pulse current flows through a heater formed of a resistance heating material, heat is generated in the heater, and ink adjacent to the heater is instantaneously heated to about 300° C. As such, the ink boils, and bubbles generated in the ink expand and apply pressure to an inside of an ink chamber filled with ink. As a result, the ink in the vicinity of nozzles is ejected through the nozzles in droplets.
Recently, to increase the printing speed of inkjet printers, sizes of printheads and numbers of nozzles have been increased. In this case, reliability and print quality can be reduced if a difference exists between an ejection ability of the nozzles. Also, a difference between a performance of printheads can occur in array printheads that are being developed to enable high speed printing. Therefore, in order to improve reliability and print quality, print abilities and performances of the nozzles of the printheads or each of the printheads of the array printheads need to be constant.
FIG. 1 is a perspective view illustrating a portion of a conventional thermally-driven inkjet printhead.
Referring to FIG. 1, the inkjet printhead is composed of a substrate 10, a chamber layer 20 stacked on top of the substrate to form ink chambers 25, and a nozzle layer 30 stacked on top of the chamber layer 20. Ink to be ejected fills the ink chambers 25, and a heater 27 is formed on a bottom surface of each of the ink chambers 25 to heat the ink inside the ink chambers 25 to generate bubbles. Nozzles 35 through which the ink is ejected are formed in the nozzle layer 30 corresponding to each of the ink chambers 25. A manifold 12 is formed on a lower portion of the substrate for commonly-supplying the ink, and ink feed holes 14 for individually supplying the ink from the manifold 12 into the ink chambers 25 are formed in an upper portion of the substrate 10.
In the conventional inkjet printhead constructed as above, less cross-talk can occur between adjacent nozzles 35 since the ink feed holes 14 individually-supply the ink into each of the ink chambers 25. In addition, a size of the printheads can be reduced since an arrangement of electrical wires is simplified. However, it is difficult to make lengths of the ink feed holes 14 the same. As a result, the lengths of the ink feed holes 14 can be different, which consequently causes a difference in an ejection ability of the ink between the nozzles 35, thereby lowering a print quality of images.
FIGS. 2A and 2B are views of simulation results illustrating ink ejection when the lengths of the ink feed holes 14 in FIG. 1 are respectively 30 and 20 μm. When the length of the ink feed hole 14 is 30 μm, a speed at which the ink is ejected is 8.97 m/s, a volume of the ink that is ejected is 4.31 pl, and a driving frequency is 28 kHz. When the length of the ink feed hole 14 is 20 μm, the speed at which the ink is ejected is 8.76 m/s, the volume of the ink that is ejected is 5.75 pl, and the driving frequency is 20 kHz. This demonstrates that the ejection abilities of the nozzles 35 are different if there is a difference in the lengths of the ink feed holes 14. As such, if the lengths of the ink feed holes 14 are different, it is difficult to manufacture inkjet printheads in which the ejection abilities of the nozzles 35 are the same. In addition, in array printheads configured to have a plurality of printheads, the amount of the ink ejected and the ejection speed of the ink differ for each printhead due to differences in the ejection abilities of the nozzles 35. Consequently, the differences in print quality among the printheads lower print quality.